Patients are selected after video-EEG monitoring to determine seizure type and focus localization. Some patients have chronic subdural recording. PET and MRI are used to study cerebral blood flow (CBF) and glucose metabolism (FDG-PET) in patients with uncontrolled complex partial seizures seizure disorders to investigate the relation of substrate supply to utilization, and the role of imaging in presurgical localization of epileptic foci. Pre- and postoperative scans are compared to assess the effect of resection on regions distant from the epileptic focus. Both LCMRglc and CBF were significantly depressed ipsilateral to the epileptic focus. However, LCMRglc was depressed by a mean of 11.2%, and CBF by only 3.2% in the lateral temporal cortex. In the mesial cortex, LCMRglc was depressed by 11.1% and CBF by 6.1%. The ratio of LCMRglc to CBF was significantly depressed ipsilateral to the focus. Using standardized criteria, blind raters found that 80% had depressed LCMRglc but only 50% of patients depressed CBF on either H215O-PET or 99m Tc~SPECT. Compared to EEG foci localized by ictal video-EEG telemetry, blood flow studies were falsely lateralizing in about 10% of patients. Using image coregistration, we compared FDG-PET to hippocampal formation volume. In this group of patients, 89% had regional hypometabolism, 61% focal T2 increases, 50% absolute HF atrophy ipsilateral to the focus. 55% had abnormal L/R HF ratios, with a smaller HF ipsilateral to the EEG focus. All patients with abnormal volumetric MRI had abnormal PET. There was a significant correlation between HF volume and inferior mesial and lateral temporal hypometabolism, suggesting that depressed LCMRglc may reflect HF atrophy. PET is more sensitive than MRI volumetry in identifying the ictal focus, but does not provide additional information when HF atrophy is present. In contrast to adults, children (mean age 14.7 years) in our series were more likely to have hypometabolism (69%) than abnormal MRI (25%). Depression among our patients, measured by the Beck Depression Inventory, was associated with reduced bilateral inferior frontal metabolism compared to both normal controls and non depressed patients with epilepsy. We are particularly interested in the value of PET scanning when surface EEG is nonlocalizing. We are analyzing data from subcortical regions with MRI based image analysis, and studying post-resection patterns of LCMRglc and CBF, to determine if there are any changes outside the resected region, which are associated with success or failure.